Automatic control equipment for substations and hydroelectric generating stations had made great strides in America, but it was little known in this country when in 1920 two 500-kW rotary converters with automatic control were ordered for tramway service in Liverpool. Accordingly the equipment was ordered from the American Westinghouse Company (with which ties were still strong), but before it arrived an order for a 250-kW plant for power and lighting service at Barrow-inFurness led M-V to develop a complete set of apparatus including relays. The Liverpool equipment, the first in this country, was the forerunner of many others, and when, for electric railways and hydroelectric stations in particular, an addition in the form of remote control from a central point appeared to be desirable the Company worked out the first' supervisory control' scheme. This was based on the use of automatic telephone gear.

METERS AND PROTECTIVE GEAR
In 1919 a meter engineering laboratory was set up for the development of new apparatus. By 1924 prepayment meters were being advocated in order to increase the domestic demand for electricity, and it was decided to design a prepayment mechanism, which became the foundation of a considerable business.

The physical size of watt-hour meters was reduced by a new design based on the type N meter; this appeared as a credit type in 1926 and as a prepayment type in the following year, and it was also built as a polyphase meter and for switchboard and consumers' service. A mercury motor type of d.c. ampere-hour meter was developed and later provided with prepayment mechanism.

Automatic protective gear was in general demand by 1920, and the Company's first important development was an inverse definite-minimum time delay relay: this was followed by a power directional relay, the two together giving complete discriminative protection on the graded time principle. Both these novelties are now included in the British Standard specification.

Subsequent developments, such as a supersensitive moving-iron relay, sensitive attracted-armature relays, the Translay differential protective system, and distance relays for line protection, gave the Company the premier position in the design of protective gear, and the start of the grid brought orders for the whole of the protective gear and metering equipment for the Central Scotland area. This gear is still working satisfactorily, almost unchanged, and today something like threequarters of all the protective relays on the grid are M-V products.